When you combine two DAAs with relatively low barriers to resistance, it

is easy for the virus to produce the double mutants that are resistant to both drugs. RBV slows this down somewhat, but does not add enough antiviral activity to prevent resistance more than 60% of the time with tegobuvir and GS 9256. There is one other factor involved in preventing resistance and that is the activity of the DAA. These extremely potent agents, which rapidly drop the viral load down to undetectable, also prevent resistance. A good example of this is the combination study of BI 201335 and BI 207127.6 This study compared two groups: BI201727 400 mg or 600 mg given thrice daily plus BI 201335 and RBV 1000-1200 mg for 4 weeks. In the 400-mg group, the RVR was 73% (with better response in genotype 1b than 1a, as

Selumetinib purchase one would expect with a protease inhibitor in the regimen). In the 600-mg group, the RVR was 100% and did not phosphatase inhibitor library differ between genotype 1a and 1b. From these data, one can infer that the potency of either the protease inhibitor or the nonnucleoside polymerase inhibitor was different, because the same two classes of drugs, plus RBV, yielded a much higher RVR. To be fair, there was no arm without RBV in this study and, of course, it is hard to compare results between studies. The designs of both studies are elegant, simple, and easy to understand, and they advance the field enormously. Gilead is now aggressively addressing the issue of

potency by adding a third DAA to tegobuvir and GS 9256 with and without this website RBV.7 The other study in this issue of Hepatology2 advances the field dramatically further. Not only does it move us from RVR without IFN to sustained virological response (SVR), but it does so in null responders! This represents a giant step toward the “Holy Grail” of HCV therapy: once-daily, oral IFN-free treatment. The world of HCV treatment changed forever in April of 2011 when the first IFN-free SVRs were presented using an NS5A inhibitor and a protease inhibitor, the same two drugs used in the Chayama et al. article.8 The 100% SVR with quadruple therapy was overshadowed by the all-oral double DAA combination (without RBV) that resulted in a 36% SVR. This was the long-awaited proof of principle that HCV could be eradicated without IFN. Notably, in the all-oral arm both of the genotype 1b patients achieved an SVR, but only 2/9 of the genotype 1a patients, demonstrating the differences in activity of protease inhibitors in genotypes 1a and 1b. The Chayama et al. study in this issue7 examined the combination of the NS5A BMS-790052 60 mg qd (now called daclatasvir) and the protease inhibitor BMS-650032 600 mg (now called asunaprevir) in null responders, but only in genotype 1b, the most common genotype in Japan. Ten patients received both drugs for 24 weeks. Of the nine patients who completed the study, all achieved an SVR.